Hallo,
ich würde mit sin(x+y) anfangen.
6sinxsin2y+3sinxcos2y+sin(x+y)cosy−cosxsinycosy
=6sinxsin2y+3sinxcos2y+(cos(y)sin(x)+cos(x)sin(y))cosy−cosxsinycosy
=6sinxsin2y+3sinxcos2y+cos2(y)sin(x)+cos(x)sin(y)cosy−cosxsinycosy
=6sinxsin2y+4sinxcos2y
=2sinx(sin2y+2sin2y+2cos2y)
=2sinx(sin2y+2)